For an illuminating device such as an LED lamp using a semiconductor light emitting element, the surface of the semiconductor light emitting element is coated with a phosphor, or powder of the phosphor is contained in the resin constructing the LED lamp to practically realize other emission colors, for example white, than the original emission color from the semiconductor light emitting element. In such illuminating device, the GaN-based semiconductor light emitting element emitting blue light with a center wavelength approximately 460 nm is generally utilized. More specifically, the surface of the GaN-based semiconductor light emitting element emitting blue light is converted to the cerium-activated yttrium aluminate (YAG) phosphor emitting yellow light to obtain white color light.
For such illuminating device using the semiconductor light emitting element, there has been such a problem that the central part of the irradiation face looks blue and a yellow ring is produced at its circumference because of passing through the blue color of excitation light, resulting in uneven coloring and non-uniform white on the irradiation face.
To solve this problem, Patent Reference 1 and Patent Reference 2 propose a structure disposed with a lens having the central emission face with a convex lens shape to emit the emission light outside, and a structure disposed with a shading member to cut the outskirts part of the emission light.
Patent Reference 3 proposes a structure a semiconductor light emitting element (LED chip) emitting ultraviolet light, a first phosphor layer comprising a blue-light-emitting phosphor absorbing the ultraviolet light and emitting blue light on the LED chip, and a second phosphor layer comprising a luteofulvous-light-emitting phosphor absorbing the blue light and emitting luteofulvous light on the first phosphor layer.
Patent Reference 1: JP A 2005-216,782
Patent Reference 2: JP A 2005-243,608
Patent Reference 3: JP A 2000-183,408